Many implantable medical devices, such as neurostimulators, pacemakers and defibrillators, transmit electrical signals to provide therapy to a patient. Electrical signals generated by the devices may be delivered to the patient tissue via electrodes disposed at a distal portion of a medical lead. The lead is electrically coupled to the device via a connector block or header of the device. The connector header includes a receptacle for insertion of the lead.
Typically, pins, which are electrically coupled to electronics of the device, are fed through a hermetically sealed housing of the device. The receptacle of the connector header contains conductive elements that are electrically coupled to the pins. The lead is insertable into the receptacle such that electrical contacts of the lead may be electrically coupled to the conductive elements of the receptacle. Conductors electrically couple the contacts of the lead to the electrodes.
Typical connector headers include a polyurethane housing and are made generally as follows. The lead receptacles are placed into the molded polyurethane housing, or alternatively, are placed into a polysulfone or other rigid polymeric frame over which the polyurethane housing is placed. Adhesive is used to bond the receptacles to the housing, the conductive elements of the receptacles are welded to the feedthrough pins, and the housing is then filled with liquid silicone rubber at low temperature and pressure. Low temperature conditions are used because polyurethane is temperature sensitive, and low pressure is to prevent distortion of the lead receptacles under during over-molding with liquid silicone rubber. Under such conditions, over-molding with liquid silicone molding takes a significant amount of time. The connector header housing is then secured to the housing of the device by inserting a barbed fastener through a bracket in the device housing and a molded hole in the polyurethane housing of the connector header.
Polyurethane, having a modulus of about 26 ksi, serves as a suitable material for a connector header housing because it does not tend to crack or craze under stresses associated with being implanted within a patient. For example, stress associated with connection of the header to the housing of the device via the barbed fastener is well tolerated by polyurethane housings. However, due to the lack of rigidity of polyurethane housings, stress associated with side-to-side deflection of the connector header relative to the device may be transferred to the feedthrough pins, resulting in feedthrough failure. More rigid polymeric materials have not been used because they are prone to cracking and crazing.